The invention relates to a battery having a plurality of battery cells which form a cell stack placed upon a bottom plate of the battery. The battery has at least one wedge for bracing the battery cells against one another.
Lithium-ion batteries which can be used as an energy store in a motor vehicle, include a plurality of battery cells typically in the form of a flat cube which are braced with a defined force. This provides safety during operation of the battery and is important with respect to the durability of the battery. A force is hereby applied upon the cell stack to thereby resist a mechanical deformation caused by the internal pressure prevailing in the battery cells.
Due to manufacturing tolerances and because the internal pressure of the battery cells fluctuates in dependence on the charging condition, ambient temperature and aging, the thickness of the cell stack may change. The cell stack thus acts at operation basically like a spring. By bracing the battery cells against one another, such changes in the thickness of the cell stack are compensated and it is ensured that they are held within mechanical limits—as specified for example by the manufacturer.
In particular when using a greater number of battery cells in the battery, the manufacturing tolerances of the battery cells placed side-by-side in the cell stack and of the bracing elements can add up to a considerable magnitude so that maintaining a required bracing force has proven difficult. Also, a decrease of manufacturing tolerances of the components of the battery is relatively complicated.
US 2009/0239137 A1 describes a lithium-ion battery with a cell stack having a plurality of battery cells and accommodated in a housing of the battery. A first sidewall of the housing bears flatly upon a side of the cell stack. An opposite sidewall of the housing extends from a bottom plate of the housing upwardly in a wedge-shaped manner. A wedge is inserted from atop into the tapered intermediate space between the cell stack and this side wall, so that the battery cells of the cell stack are braced against one other. The inserted wedge is secured by a screw passed through the wedge-shaped sidewall.
In U.S. Pat. No. 7,241,530 B2, which also relates to a lithium-ion battery, two complementary wedges are arranged in a battery housing which accommodates the cell stack, one of which resting against one side of the cell stack and the other one of which on a rib formed on a sidewall of the housing.
Furthermore, WO 2005/045981 A1 discloses a method for bracing fuel cells of a fuel cell stack by means of tie bolts which extend through an upper end plate and are screwed to an opposite lower end plate. A pressure plate provided with conically tapering marginal areas is situated between the upper end plate and the stacked fuel cells. By tightening setscrews, which are passed through lateral legs of the upper end plate, two wedges can be inserted from outside between the conical marginal areas and the end plate to thereby increase the force for bracing the fuel cell stack.
Constructions known in the art for bracing the cell stack of a battery have shown to be comparably cumbersome when it comes to achieving fixation of the components of the battery.